The present invention relates to thermal printers for printing labels conveyed on a web; more particularly, the invention relates to a mechanism for moving a print head into and out of engagement with a platen and for engaging and disengaging a ribbon take-up spool.
The invention is related to the device disclosed in U.S. Pat. No. 4,910,675, issued Mar. 20, 1990, which discloses a processing and packaging system for prerecorded computer diskettes including a label printer and applicator, a diverter, a sleever, and a stacker. The present invention relates to a printer of the type to be utilized in printing the labels for diskettes.
Thermal printers of the type of the present invention utilize a row of thermal elements mounted on or as part of a print head. The print head is engaged with the platen with a print medium between the print head and the platen. As the print medium is passed between the print head and the platen particular elements are electrically heated creating an image on the heat-sensitive medium. With the printer of the type associated with the present invention a heat-sensitive ribbon will be positioned between the print head and the web of labels. It is desirable to have the printer capable of printing and applying thirty labels or more per minute.
Typically, in thermal printers, the print head will remain continually engaged with the platen except when the print head is lifted to insert a new web.
In printing a web of adhesive labels where each label is to be applied to diskettes immediately after printing, the web moves forward and rearward and the spaces between the labels present an uneven web thickness. The movement and the uneven web thickness can cause significant wear on the thermal elements if the print head remains engaged with the platen. Additionally, the engagement can interfere or restrict the movement of the web and ribbon affecting the speed of the printer. Additionally, moving the web and label without raising the print head can inadvertently transfer ink to the label. Furthermore, the ribbon used in these types of printers is thin and fragile and could easily be damaged by such motion. Thus, it is efficacious to raise the print head between the printing operation for each label. One means of raising the printer head is through the use of an electric solenoid. Solenoids have significant disadvantages: they generate heat, they consume excessive amounts of electric power; and have nonuniform force through their stroke.